Direct fuel injection (DI) systems provide some advantages over port fuel injection systems. For example, direct fuel injection systems may improve cylinder charge cooling so that engine cylinders may operate at higher compression ratios without incurring undesirable engine knock. However, direct fuel injectors may not be able to provide a desired amount of fuel to a cylinder at higher engine speeds and loads because the amount of time a cylinder stroke takes is shortened so that there may not be sufficient time to inject a desired amount of fuel. Consequently, the engine may develop less power than is desired at higher engine speeds and loads. In addition, direct injection systems may be more prone to particulate matter emissions.
In an effort to reduce the particulate matter emissions and fuel dilution in oil, very high pressure direct injection systems have been developed. For example, while nominal direct injection maximum pressures are in the range of 150 bar, the higher pressure DI systems may operate in the range of 250-800 bar using a high pressure piston pump that is mechanically driven by the engine via a camshaft. In engines configured with dual injection systems, that is engines enabled with both direct and port fuel injectors, pressurized fuel from the fuel tank may be supplied to both the direct injection high pressure fuel pump (HPFP) as well as the port injection fuel rail. In order to reduce hardware complexity, the fuel may be supplied to the port injection fuel rail either through the HPFP, or may be branched off before the pump, thereby reducing the need for a dedicated pump for the port injection fuel rail.
However, one issue with such dual fuel injection system configurations is that fuel pulsations from the high pressure fuel pump may enter the port injection fuel rail. This is due to the sinusoidal fuel pressure generated at the high pressure fuel pump due to the pump being driven by the engine via a camshaft (and cam lobes). The pulsations may worsen when the HPFP is not flowing any fuel into the direct injection fuel rail (such as when direct injection is disabled) due to the pump returning all of the ingested volume back into the low pressure region of the fuel system. The pulsations in the port injection fuel rail can lead to larger discrepancies between the value of rested fuel in the port injection fuel rail as compared to value of fuel injected from the port injection fuel rail. As such, this can result in large fueling errors.
In one example, the above issue may be at least partly addressed by a method for an engine, comprising: pressurizing fuel in a port injection fuel rail via an engine camshaft driven high pressure fuel pump; and injecting a port fuel injection with a timing balanced around an average pressure-crossing of port fuel injection pressure. In this way, fueling errors due to fuel pump induced pressure fluctuations in the port injection fuel rail are reduced.
As one example, an engine system may include an engine-driven high pressure fuel pump supplying fuel to each of a port and direct injection fuel rail. The fuel pump may be a piston pump coupled to the engine via each of a camshaft and cam lobes, and due to this configuration, the fuel pressure in the fuel pump may vary in a sinusoidal manner. This may in turn cause sinusoidal fluctuations in a fuel pressure in the port injection fuel rail. An engine controller may estimate the pressure in the port injection fuel rail based on the pressure at the fuel pump, and further based on an engine speed dependent fuel pulse delay. The controller may estimate the timing (with respect to engine position) of local maxima and local minima in the waveform of the port injection fuel rail pressure, and accordingly determine the position of zero-crossings of the waveform. An initial timing and width of a port fuel injection pulse may be determined based on engine operating conditions including, for example, intake valve opening (IVO) and fuel flow velocity through the fuel system to allow for a closed intake valve injection. The timing of the port injection fuel pulse may then be moved to coincide with the timing of a first zero-crossing in the advanced direction. In addition, the initial pulse width of the port injection fuel pulse may be adjusted based on the adjusted timing to compensate for any difference in fuel puddle dynamics.
The technical effect of centering a port fuel injection pulse around a zero-crossing of a fuel rail pressure waveform is that under-average pressure changes can be cancelled out by over-average pressure changes. By moving the middle of injection angle of the port injection fuel pulse to coincide with an average pressure at the first zero-crossing in the advanced direction, closed intake valve port fuel injection can be maintained while port injection fuel rail pressure fluctuations induced by sinusoidal changes in a fuel pump pressure are substantially removed. By relying on the average port injection fuel rail pressure, the need for fast fuel pressure sampling is reduced. In addition, pressure fluctuations can be addressed without requiring additional pressure dampeners, check valves, or orifices. Overall, metering of fuel from the port injection fuel rail is improved while removing the need for a dedicated fuel line for the port injection fuel system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.